The Sun Chronicle, a daily newspaper in Attleboro, Massachusetts, has this article on the 25 groups that have asked Massachusetts election officials to keep track of how many registered members they have.
The story doesn’t actually explain to its readers why Massachusetts lets groups file to have their registrations tallied. Starting in 1991, any group that has registration of at least 1% of the total state registration becomes a newly-qualified party. No group has ever managed to achieve 1%.
Other states in which unqualified parties can file to have their registrations tallied are Alaska, California, Iowa, Kentucky, Maine, New Jersey, and New York. Sometimes the request must be accompanied with other requirements. New York only keeps the tally for groups that had a statewide candidate on the ballot in a gubernatorial election; Iowa only does it for groups that submit 950 signatures on a petition. Delaware and Louisiana keep track of registration in every group, whether that groups asks for a tally or not.